P05 –Comparative exploration of KEA3 function in PMF partitioning and photoprotection

叶绿体PMF是通过光驱动的质子耦合电子传递穿过类囊体膜产生的。这产生了膜电位（膜电位）和质子浓度梯度（质子pH）。它们对PMF的贡献部分取决于类囊体离子转运过程。PMF的pH值分量，或者更具体地说，内腔质子浓度决定了用于光化学的光能的分数。我们从拟南芥（Arabidopsis thaliana）的数据表明，类囊体K +-交换反向转运蛋白3（KEA3）在光波动期间维管植物光合作用的灵活性中起着重要作用。KEA3可以感知叶绿体基质的能量状态，并调节光保护能量依赖性猝灭（qE）机制的水平。如果能量状态低，KEA3被激活以降低管腔的质子浓度并关闭QE。虽然KEA3活性影响PMF组合物并降低PMF pH组分，但它似乎对PMF大小及其能量功能几乎没有影响。以前，我们可以证明，去调节KEA3活性可以导致瞬时更高的CO2固定率。这提出KEA3调节作为在自然界中发现的动态光条件下增强光合作用的假定目标。深入了解KEA3调节及其与光合反应复杂网络的相互作用将是进一步探索这一途径的关键。在GoPMF的框架内，我们寻求通过比较方法扩展我们对KEA3在PMF分区及其调节中的功能的了解：（i）通过测量单细胞莱茵衣藻（Chlamyeliumreinhardtii）中的KEA3活性，（衣原体），我们的目标是了解KEA3功能和调节的进化效应，（ii）通过比较拟南芥和衣原体之间的基质能量动态，我们的目标是表征环境变化如何影响叶绿体能量状态并将其与KEA3活性联系起来，（iii）通过确定KEA3调节因子，我们将基质能量状态的变化与KEA3活性联系起来，最后（iv）通过在植物中表达修饰的KEA3形式，我们将通过实验来证实这些联系，并利用我们对KEA3调节PMF的知识来尝试改善光合性能和生长（参见第5页摘要）。我们的工作将是GoPMF 2目标的组成部分，并为目标1，3，4和5做出贡献。

The chloroplast PMF is produced via light-driven proton-coupled electron transport across the thylakoid membrane. This generates both a membrane potential (∆ψ) and a proton concentration gradient (∆pH). Their contribution to PMF is governed in part by thylakoid ion transport processes. The ∆pH component of the PMF or more specifically, the lumenal proton concentration determines the fraction of light energy that is used for photochemistry. Our data from Arabidopsis thaliana (Arabidopsis) show that the thylakoid K+-exchange antiporter 3 (KEA3) plays a fundamental role for the flexibility of vascular plant photosynthesis during light fluctuations. KEA3 can sense the energy state of the chloroplast stroma and adjusts levels of the photoprotective energy dependent quenching (qE) mechanism in response. If the energy state is low, KEA3 gets activated to decrease the proton concentration of the lumen and shuts off qE. While KEA3 activity affects PMF composition and decreases the ∆pH component, it appears to have little effect on PMF size and thus its energetic function. Previously, we could demonstrate that de-regulated KEA3 activity can result in transiently higher CO2 fixation rates. This proposes KEA3 regulation as a putative target for enhancing photosynthesis under the dynamic light conditions found in nature. An in-depth understanding of KEA3 regulation and its interaction with the complex network of photosynthetic reactions will be pivotal to further explore this avenue. Within the framework of GoPMF, we seek to extent our knowledge of KEA3 function in PMF partitioning and its regulation via a comparative approach: (i) By measuring KEA3 activity in the unicellular alga Chlamydomonas reinhardtii (Chlamydomonas), we aim to understand evolutionary effects on KEA3 function and regulation, (ii) by comparing stromal energy dynamics between Arabidopsis and Chlamydomonas, we aim to characterize how environmental changes affect the chloroplast energy state and relate this to KEA3 activity , (iii) by determining KEA3 regulating factors, we will link changes in the stromal energy state with KEA3 activity and finally (iv) by expressing modified KEA3 versions in planta, we will confirm these links experimentally and use our knowledge on PMF modulation by KEA3 for attempts to improve photosynthetic performance and growth (see also Graphical Abstract P05). Our work will be integral for the aim GoPMF 2 and additionally contribute to aims 1, 3, 4 and 5.